Fuzessery Z M, Hall J C
Department of Zoology and Physiology, P.O. Box 3166, University of Wyoming, Laramie, WY 82001, USA.
Hear Res. 1999 Nov;137(1-2):137-54. doi: 10.1016/s0378-5955(99)00133-1.
Neurons selective for sound duration have been reported in the auditory midbrain and cortex of several specialized vertebrate species that process behaviorally relevant signals of stereotypic duration. This study examines duration selectivity in the inferior colliculus (IC) of the pallid bat to determine if this selectivity is limited to regions that serve echolocation, or if it extends to low-frequency regions that serve passive listening. It also focuses on the temporal response properties of duration-selective neurons to elucidate mechanisms that may underlie the creation of this selectivity. Of 140 neurons tested, 36% were selective for short durations of </=7 ms, and acted as short-pass or bandpass duration filters. Sixteen percent, termed long duration neurons, differed in that they required minimum sound durations of 5-50 ms before responding, and all acted as long-pass duration filters. Short duration neurons were equally common in the high-frequency region serving echolocation and the lateral low-frequency region that serves passive listening, indicating that selectivity for short duration sounds was not associated only with the specialized function of echolocation. Long duration neurons were most common in the medial low-frequency region IC. Selectivity for short and long duration sounds was therefore not uniformly distributed across the IC. Analyses of the temporal response properties of short duration neurons, and the application of bicuculline to block gamma-aminobutyric acid-A receptors, were used to infer the synaptic interactions that underlie the creation of duration selectivity, the role of inhibition in its creation, and whether a coincidence mechanism proposed by Casseday et al. (Science 264 (1994) 847-850) is consistent with the behavior of the duration-selective neurons recorded in the pallid bat IC. Present results suggest that while some neurons do behave in a manner that is consistent with the coincidence mechanism, the behaviors of others suggest that more than one mechanism may create a selectivity for short duration sounds.
在几种专门处理具有刻板时长的行为相关信号的脊椎动物物种的听觉中脑和皮层中，已报道存在对声音时长具有选择性的神经元。本研究考察了苍白蝠下丘（IC）中的时长选择性，以确定这种选择性是否仅限于服务于回声定位的区域，或者是否延伸至服务于被动聆听的低频区域。研究还聚焦于时长选择性神经元的时间响应特性，以阐明可能构成这种选择性基础的机制。在测试的140个神经元中，36%对时长小于等于7毫秒的短时长具有选择性，并充当短通或带通时长滤波器。16%的神经元被称为长时程神经元，不同之处在于它们在做出反应前需要5 - 50毫秒的最短声音时长，并且全部充当长通时长滤波器。短时长神经元在服务于回声定位的高频区域和服务于被动聆听的外侧低频区域中同样常见，这表明对短时长声音的选择性并非仅与回声定位的特殊功能相关。长时程神经元在IC的内侧低频区域最为常见。因此，对短时长和长时长声音的选择性在IC中并非均匀分布。对短时长神经元的时间响应特性进行分析，并应用荷包牡丹碱阻断γ-氨基丁酸-A受体，以推断构成时长选择性基础的突触相互作用、抑制在其形成中的作用，以及Casseday等人（《科学》264 (1994) 847 - 850）提出的一种巧合机制是否与在苍白蝠IC中记录的时长选择性神经元的行为一致。目前的结果表明，虽然一些神经元的行为方式与巧合机制一致，但其他神经元的行为表明可能有不止一种机制产生对短时长声音的选择性。
